The key differentiation between open-source software and proprietary software lies in source code access. Open-source software is released under licenses that allow users to view, modify, and distribute the source code freely. This promotes collaboration and community contributions, resulting in rapid development and innovation. In contrast, proprietary software restricts access to its code, typically requiring users to purchase licenses and limiting their ability to modify or redistribute the software. This model often emphasizes control and corporate ownership, while open-source focuses on collaboration and user empowerment.